Notizen:
The Encapsulated Security Payload protocol (ESP) is like the AH protocol an IP protocol. ESP is the protocol 50.
ESP offers authentication, integrity checking and confidentiality by encryption. Encryption is not enforced by the protocol. The available encryption algorithms include null, DES and 3DES.
FreeS/Wan does not implement DES.
Authentication is based on MACs. But in contrast to AH the IP header is not authenticated.
Additionally ESP may use sequence numbers to protect against replay attacks.